1. Field of the Invention
The present invention relates to a method of manufacturing a circuit device, and more particularly to a method of manufacturing a circuit device (SIP or ISB) in which a circuit element is covered with and supported by an insulating resin without providing a supporting substrate.
2. Description of the Related Art
Recently, instead of separately packaging each semiconductor element as was previously done, techniques are developed in which a plurality of circuit elements such as an IC, an LSI, and a chip resistor are packaged in one package and supplied as a system. These techniques are known as SIP (System in Package) or ISB (Integrated System in Board). Techniques for providing a system as one package can generally be classified as one of a PCB mounting, system LSI, or ISB technique. PCB mounting suffers problems in that it is difficult to reduce the size and weight and to obtain high performance. Although a system LSI has advantages that it is possible to reduce the size and weight, to obtain high performance, and to reduce power consumption, the system LSI suffers problems in that changes to the specification are difficult and development of a new system is very expensive. On the other hand, the ISB has the advantages of the system LSI in that it is possible to reduce size, weight, and power consumption and, in addition, has an advantage that it is possible to quickly respond to a change in the specification. More specifically, while in a system LSI, an SOC chip in which a plurality of functions are integrated is formed and mounted on a substrate, in an ISB, a system is constructed by connecting a plurality of chips by a multi-layer wiring. Thus, it is possible to flexibly respond to changes in specifications by changing the chip and wirings in an ISB.
FIGS. 16 and 17 show respectively a perspective view and a side view of an ISB circuit device. In an ISB circuit device, unlike in a PCB mounting, a plurality of circuit elements are embedded into an insulating resin package and there is no supporting substrate such as a print substrate in the PCB mounting. A circuit element such as an LSI bare chip 52A, a chip CR 52B, and a Tr bare chip 52C are fixed onto a conductive path 51 such as a copper pattern using a conductive paste 55B and are covered and integrally supported by an insulating resin 50. In other words, the insulating resin 50 functions to cover the plurality of circuit elements, and, at the same time, as a supporting member of the circuit elements. The LSI bare chip 52A or the like are wire-bonded by a gold line bonding 55A. The conductive path 51 is exposed on the backside of the ISB circuit device and a solder ball 53 is connected.
FIGS. 18–21 show a method for manufacturing an ISB circuit device. As shown in FIG. 18, a sheet-shaped conductive foil 60 is prepared and a photo resist (etching-resistive mask) PR is formed on the conductive foil 60, and the photo resist PR is patterned so that the conductive foil 60 exposes in regions other than a region which forms the conductive path 51.
Next, as shown in FIG. 19, the conductive foil 60 is etched using the photo resist PR as a mask to form a separation channel 61. The thickness of the conductive foil 60 can be set in a range from 10 μm to 300 μm (for example, 70 μm) and the depth of the separation channel 61 can be set to, for example, 50 μm. As the etching, for example, a wet etching process, a dry etching process, and evaporation by laser can be employed.
Then, as shown in FIG. 20, circuit elements such as the LSI 52A and chip CR 52B are mounted on the conductive foil 60 on which the separation channel 61 is formed. The bare LSI chip 52A is fixed by a conductive paste 55B and the chip CR is fixed by a soldering member such as solder or by a conductive paste. The terminal of the LSI 52A is wired by a metal fine line 55A.
Next, as shown in FIG. 21, an insulating resin 50 is attached to the conductive foil 60 and the separation channel 61. The insulating resin 50 is an epoxy resin, a polyimide resin, or the like, and is formed through transfer molding or injection molding. The thickness of the insulating resin 50 covering the surface of the conductive foil 60 is adjusted, for example, such that approximately 100 μm from the top portion of the circuit element is covered. Then, the backside surface of the conductive foil 60 is chemically or physically removed and separated as the conductive path 51. In FIG. 21, a surface exposed by the removal is shown by a dotted line. For example, the conductive path 51 is separated by grinding the backside surface by approximately 30 μm using an abrasive or a grinder. Finally, a solder ball is connected to the exposed conductive path 51 to complete the ISB circuit device. The above manufacturing steps shown in FIGS. 18 to 21 are automated, so that when mask data for forming a mask pattern shown in FIG. 18, part arrangement data, and wire bonding data are provided, the ISB circuit device can be manufactured automatically.
FIGS. 22A, 22B and 22C show another ISB circuit device 70. As shown in FIG. 22A, in this circuit, a current mirror circuit made of transistor chips TR1 and TR2 and a differential circuit made of transistor chips TR3 and TR4 are integrated. Four transistor chips TR1–TR4 are bonded by a Au fine line. As shown in FIG. 22C, a die pad 71 on which a Z film (a film having a larger growth in the thickness direction than in the planar direction) 74 is formed, a bonding pad 72 on which a Z film 74 is formed, a die pad, and a bonding pad are electrically connected by a wiring 73. As the wiring 73, a rolled copper foil may be used. Because the rolled copper foil is resistive against repetition of bending by heat, the rolled copper foil inhibits disconnection of the wiring.
Additional explanation can be found in Japanese Patent Laid-Open Publications Nos. 2001-217338 and 2002-93847.
As described above, ISB circuit devices have various features. Conventionally, a user who wishes to have such an ISB circuit device, such as, for example, a device manufacturer, which as used herein refers not just to manufacturers of electronic goods in their final form, but also to intermediate manufacturers and assembler of components, provides an ISB mounting manufacturer with a specification document or the like which describes the specifications to be satisfied by a desirable ISB. The ISB mounting manufacturer then performs circuit design, pattern design and also mask design based on the specifications, so that an ISB circuit device is manufactured according to the above steps shown in FIGS. 18 to 21. However, there is a demand for a method in which a user can obtain an ISB circuit device more promptly and effectively. Especially, a device manufacturer, who manufactures a product having a short life cycle, has a strong demand for such a method.